A little more info on the DNS...
The naming structure is: sub-child.child.parent.god
This is why mail comes from mailserver.yourdomain.com, and why the client computers are going to be workstation.yourdomain.com. That .com at the end tells that its a corporate network. "yourdomain" is that name you wound up registering when the one you really wanted was taken by someone else. If you have a server named "local" then this will AUTOMATICALLY be local.yourdomain.com if it belongs to "yourdomain.com" So if you put the "local" anywhere BUT at the end, you are in effect creating a sub-domain that someone COULD try to reach (I know there is a local.net, so if you were to use yourdomain.local.net you would be a child of someone else's domain. I had this happen on my test network a year ago, where my server accidentally wound up a child of another domain. I had the strangest DNS records appearing...replicating from the "parent" domain, and when I wanted to add my own records they took forever to resolve...I was populating another domains DNS servers! Big security issues there!)
Your clients will end being workstation1.yourdomain.com they will not correctly resolve
You will have to add records to your internal DNS server telling the clients the private IP address 192.168.1.XXX while the external DNS knows this web site by the public IP 90.1.1.XXX. Your clients can wind up trying to use two different name records at different times, which makes for strange client problems that would only occur depending upon the cached DNS records. Diagnosing these cache records errors can require tremendous effort.
Now, if you put .local at the END, you have created a entire new structure that cannot be associated through any external connection (because there is no nameserver for ".local" like there is or ".com, .bis, .name, etc.) Actually you don't need to use .local at all, ANYTHING except a valid register will be fine (i.e. DNSserver.mydomain.franklindelanoreroosevelt), M$ has decided that .local is what they will automatically attach if you choose that selection box...
Alex